Finding and Acquiring Data

There area huge number of web sites with spatial data. The challenges are:

• Finding the the data
• Making sure the data is appropriate for what you want to use it for
• Downloading data data
• Converting the files to be usable in a GIS (unzip, file format conversions)
• QAQC: Including making sure the spatial reference is correct
• Projecting the data into your desired spatial reference
• Documenting the data so it can continue to be used in the future (editing metadata)

Finding Data

There are standard web "portals" and "warehouses" for data. Search the web for "Shapefile <your interest>" or "GIS Data <your interest>." You can also talk to other GIS folks about where the good data is and how to get it.

Downloading data from the Humboldt County web site.

Making sure the data is appropriate for what you want to use it for

Whether the data is appropriate for what you want to use it for can depend on:

• How the data was collected
• The uncertainty (or error) in the data
• Use restrictions

Before downloading the data, it is a good idea to look around the web site to see if there are any indications if the data is not appropriate for your use. This will save you time. After you download the data, check any associated metadata for additional information. If you are unsure, it's best to contact someone at the organization that manages the data.

Downloading the Data

1. Download the data, which could take a few minutes to several days.
2. Un-compress the data and save it locally with documentation.

Saving it locally simply refers to placing the data into a file-folder structure that is organized so that you can find it again at a later time. For this class, we always save it into the "1_Originals" folder.

Converting the files to be usable in a GIS

Most GIS data comes in compressed file formats such as "zip", "gz", and "tar". After uncompressing one of these files you may find another compressed file. Keep going until you find the actual data files, then throw away the compressed versions.

Some of the file formats used for distributing data are not supported by all GIS applications (like GeoDatabases, MS-Access database files, and others). You may need to obtain access to another application or a special utility to convert these data sets to standard GIS file formats (like Shapefiles, TIF files, and IMG files).

QAQC: Making sure the spatial reference is correct

After you've downloaded the data, put it through a formal QAQC check. This should include:

1. Checking the spatial reference
   1. Define the spatial reference correctly if it is missing or incorrect
2. Perform a visual inspection
3. Check the metadata
4. Perform other checks as needed

Projecting the data into your desired spatial reference

If you don't already have one, create a folder in the "2_Working" folder for the spatial reference you want to use for the project. Examples would include "WGS_84_UTM_Zone_10_North" and "NAD83_State_Plane_California_Zone_I_Meters".

• If the data is in your desired spatial reference:
  • Copy it into the "2_Working" folder
• Else
  • "Project" it into your desired spatial reference and into the "2_Working" folder

Documenting the data so it can continue to be used in the future

The data you process will often be used by others in the future so remember to document the data as you go. If you make changes to the data, you now are a holder of a copyright to the data. The original copyright holders are also still holders of the data as well.

Note: GIS Applications like ArcMap will add information on the processing steps taken to create a particular data set. You can maintain these in the metadata if desired and/or add more "human-readable" text for others to read.

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